Acetylcysteine is an antioxidant having a molecular weight of 163.2 and the following chemical structure:
(Merck Index 13th ed., n90, page 17). Acetylcysteine is marketed generically in the United States and worldwide, as well as under the trade names of Acetadote®, Mucomyst®, Parvolex®, Fluimucil®, and others. It is approved for several indications including treatment of acetaminophen overdose, as an injectable and an oral agent, and as a mucolytic, as an inhalation product. Acetylcysteine is also being used or investigated to treat other indications including liver failure, various cancers, methacrylonitrile poisoning, reduction of radiocontrast-induced nephropathy, and reduction of reperfusion injury during cardio bypass surgery.
Acetylcysteine is not a stable molecule and is oxidized and degraded when in solution and exposed to air. Several U.S. patents have addressed this problem. For example, U.S. Pat. No. 5,691,380 appears to describe the use of a topical silicone-based emulsion system to improve the stability of acetylcysteine.
Other U.S. patents appear to address the problem by using a chelating agent to stabilize the acetylcysteine. Chelating agents, or chelators, are organic agents that bond with and thereby sequester free metal ions from solution. A widely used chelator is edetic acid or ethylenediaminetetraacetic acid, commonly referred to as EDTA, which has a molecular weight of 292.24 and the following chemical structure:
(Merck Index 13th ed., n3546, pages 620-621). EDTA is available commercially as the free acid and as various salts, for example disodium EDTA, tetrasodium EDTA, dipotassium EDTA, and calcium disodium EDTA.
U.S. Pat. No. 5,807,894, for instance, appears to describe the use of the chelating agent EDTA to improve the high reactivity of acetylcysteine in a syrup formulation. U.S. Pat. No. 6,114,387 appears to describe the use of EDTA to stabilize acetylcysteine in a solid dosage form. Aqueous solutions of acetylcysteine on the market, such as those under the trade names of Acetadote®, Mucornyst®, Parvolex®, Fluimucil®, also contain EDTA, in the form of the salt disodium edetate, which aids in stabilizing the pharmaceutical product.
While improving the stability of acetylcysteine formulations, chelating agents such as EDTA can cause undesirable effects when administered to humans or animals. Some of these undesirable effects include a significant drop in serum calcium levels (Handbook of Pharmaceutical Excipients 226 (R. Rowe et al. eds., 4th ed., 2003)), which may result in fatality, hypokalemia, hypomagnesemia, hypotension, and EDTA has also been shown to produce reproductive developmental toxicity in test animals. EDTA has also been associated with dose-related bronchoconstriction when used as a preservative in nebulizer solutions. Id. Based on the adverse effects of EDTA, particular care should be taken when administering EDTA to patients with renal impairment, liver toxicity, tuberculosis, and impaired cardiac function. Id.
Since acetylcysteine may be used to prevent or treat a variety of disorders and conditions, including liver damage, the addition of a chelating agent such as EDTA to an acetylcysteine pharmaceutical product is of concern. Chelating agents, while stabilizing the acetylcysteine composition, may also decrease the effectiveness of the composition. In addition, some individuals are allergic to chelating agents such that they cannot receive acetylcysteine compositions containing a chelating agent or may require additional care after receiving such compositions.
It would therefore be desirable to have a stable acetylcysteine solution drug product that does not produce adverse effects upon administration. In certain conditions, such as the use of acetylcysteine to lessen or prevent the liver damage caused by acetaminophen overdose, removing EDTA or other chelating agents could improve efficacy by limiting any additional liver toxicity resulting from the chelating agent.